No, an OEM version is not locked to a hardware manufacturer. If the system comes with some sort of restore disc, that IS locked to that system configuration because it's a copy of the system state after it rolled off the assembly line. A true Windows OEM disc has no software/hardware locks in it.
Yes, you can use an OEM copy of Windows could be used to load an upgrade version. Whether or not that violates licensing is another separate issue (not that MS should care, retail upgrades cost as much as if not more than OEM full versions). Simple fact is that there is no lock tying Windows to particular hardware (other than the obvious meeting of system requirements.).
I know that a restore disk can re-image the HD back to the way it came from the factory. But the ones I seen can also just re-install Windows. Without altering any other software you have on the HD. And you can actually see it go through the install process of Windows. Not re-image it. But you can not use this disk to install Windows on any other PC. Even if you can supply the drivers needed on the other PC.
I know you can use an upgrade version of Windows to upgrade the OS on the computer the OEM disk or "restore disk came with. But can you use either one of them as proof of a previous version of Windows on a computer that you built from scratch? (Say that your Dell dies.) Will an upgrade version of Windows accept this OEM (or restore) disk when it ask you to put a previous Windows disk in the drive so it can verify you have a previous version? If not, then that OEM disk essentially locked you to the PC it came with. And you can only upgrade the OS on that PC with that license.
And in reality, many PC's now comes with the restore software an HD partition. They no longer supply you with a "disk". So your Windows license is only good for that PC and is not transferable to another PC. If the HD dies, so does your Windows license.
Yes there is a difference. How soon some people forget. MS is a monopoly and must be treated as such. MS would run into problems with the DOJ if it tries to do that. And if they could do it, many PC makers would complain. Because if MS could lock out one vender, then what prevents MS from locking out any of the other venders. This would increase MS monopolistic power greatly.
For a great many computer users, there is no other viable choice except Windows. That is not the case with OSX. You can nearly do everything that you do on a Mac (with OSX), on a PC (with Windows). The reverse is not true, as so many PC people have pointed out, because there are much more software that peole depend on, that can't run on OSX.
But what if there were a half of dozen OS's to choose. With many cross compatible software. And MS wasn't a monopoly it terms of market share. Would there be a problem if MS decided to make their OS available only on Dell hardware? Or if Dell decided to buy out MS and use their OS only on their PC's. I don't think so. Now people that like to use Sony or HP hardware might complain. And other PC makers will complain. But so long as there are other viable OS's to choose from they most like couldn't stop it.
What if Dell contract out MS to write them an optimized version of Windows for Dell brand PC's. Can anyone stop Dell and MS from going through with this? So long as MS maintains a version of Windows for all the other PC makers.
And what if some PC maker wants to make and sell a specialize PC and develops an OS for it. Would that company also have to make their OS available to all PC makers just because they share similar hardware?
Suppose you develop a killer OS for a tablet PC. Can anyone stop you from selling that OS to HP and lock out all other venders if HP paid you enough for the rights to use it?
What if you went out an built a game console using nearly the same components as an Xbox. Would you be able to force MS to give you their Xbox OS so that you can do a little modification and use it on your console? Could you buy old broken down Xboxes for $50.00 and remove the eprom chip that the Xbox OS is on use it in your consoles? And then sell your Xbox game compatible consoles. Because MS owns the rights to their Xbox OS. Buying an Xbox only gets you the license to use their OS on that Xbox.